This invention relates to a printed circuit board and more particularly to the shape of copper foil pattern formed thereon. Printed circuit boards are generally manufactured by inserting various components from one side of a board and then mounting parts such as display tubes and flat LSI circuits on the other side. Many methods of automating this process have been considered such as the use of a soldering iron, soldering with heated air, laser beam soldering and soldering by exposure to a lamp. For a high-quality soldering work, however, it is critically important to be able to supply solder at an optimum rate. For this reason, attempts have been made to apply creamy solder to specified soldering positions preliminarily by using a dispenser, by screen printing and by stamping. With any of these methods, however, it is difficult to apply the creamy solder uniformly because it frequently happens that the viscosity of solder changes during the process, foams are developed inside the dispenser, nozzles become clogged or the amount attached to the stamp fluctuates. For the purpose of applying the solder uniformly, furthermore, care must be taken to ascertain before creamy solder is applied to the board that there is no residual solder present at the positions of interest because the amount of such residual solder is totally unpredictable. For this reason, extra processes become necessary such as preliminarily applying a masking agent to prevent solder from attaching and peeling it off after dip soldering is finished. Moreover, the flux contained in creamy solder is extremely active with high basicity and copper foil patterns and mounted components must be protected from its corrosive effects by washing but washing is done manually in almost all cases. In summary, methods of using creamy solder are expensive to operate because there are at least four additional processes to be included, that is, application and removal of masking agent, application of creamy solder and washing. In addition, use of expensive creamy solder, masking material and washing agent adds to the cost of the operation.
In view of the above drawbacks, methods of making effective use of the solder which becomes attached by the dip soldering process have been considered, but since the amount of solder which becomes attached is completely unpredictable, a so-called hot air knife method may be utilized whereby excess solder is blown off by a hot wind of about 273.degree. C. or above immediately after the dip soldering. By this method, however, too much solder is sometimes blown away and holes are left behind.
According to still another method, a router is used after the solder hardens to scrape it off mechanically. The amount of solder thus scrapped is not always constant, however, because of thermal distortion due to the heat of soldering and this happens in particular in the case of a single-side circuit board. In addition, there remains the problem of the scraped solder pieces scattering all over and this method is also expensive to operate.